The goal of this study is to characterize the role of the small intestine in human zinc homeostasis with special reference to post-prandial secretion-reabsorpption of endogenous zn. This objective will be achieved by a combination of multi-lumen intestinal intubation/perfusion stable isotope kinetic and model based compartmental analysis techniques. These techniques will be used for quantitative evaluatio of zn homeostasis in the small intestine over a range of dietary zn intakes in normal subjects and in patients with cystic fibrosis.